In view of the phenomenon that heat exchange efficiency of the diesel hydrocracking high pressure heat exchangers in a refinery reduced and scaling in reactor inlet distributor and other equipment,the sampling analysis was conducted accompanied by shutdown of hydrocracking unit.The X-ray fluorescence spectrometer（XRF）,scanning electron microscope（SEM） and X-ray diffractometer（XRD） etc.were carried out to analyze scale sample after toluene extraction.The results showed that the scale was composed of relatively loose structure and a layer of compact structure,and the loose structure was mainly composed of scales containing Fe and S elements,but Cr,Fe,S and O elements for scales of compact structure.The main inorganic components of scale were Fe（x）S（y） and Fe（x）Ni（z）S（y）.In addition,it also contained a small amount of inorganic materials containing Si,Na Al,and little organic scale could be ignored.In this regard,it is suggested that the refinery should inject scale inhibitor to inhibit the scaling rate of high pressure heat exchanger or other equipment,and realize controllable scaling rate by tracking and calculating the scaling resistance of heat exchangers.The heat exchangers will be cleaned depending on the scale when the equipment is normally shut down for maintenance.